1. Field of the Invention
The present invention relates to a charge domain signal filter applicable to a communication apparatus or a signal processing unit.
2. Description of the Prior Art
Heretofore, digital signal processing technology represented by DSP, as shown by the composition of digital filter system illustrated in FIG. 19 has been made an extremely great progress in terms of its processing speed and resolution according to a rapid progress of MOS semiconductor integrated circuit technology.
However, needs for higher level operations using circuits with increased complexity have provoked new problems such as increase of power consumption or device heat generation and, combined with technical needs such as miniaturization or portability, the development of new technical approaches is strongly required.
Revaluation of analog processing method, utilization of analog circuit of low power consumption where allowed functionally or other trends may be as much aspects of this requirement.
In the past, the analog processing has been considered generally "to be low in accuracy, hard to realize integrated circuits and often requiring a large circuit area"; however, some analog circuits are proposed for the operation circuit acting in charge domain wherein the power consumption is low and, moreover, the same function may be ensured by a circuit substantially smaller than the digital circuit in some applications, thus representing as much examples of new technological approaches meeting with such trends.
Conventionally, inventions concerning such apparatus are disclosed in U.S. patent application Ser. No. 08/344,650, U.S. Pat. No. 5,539,404 or U.S. Pat. No. 5,537,115.
On the other hand, conventional digital filters have been proposed in 4 typical compositions shown in FIGS. 20 to 23.
FIG. 20 shows the composition of a filter of the type called FIR (Finite Impulse Response Type) without using feedback from output signal, FIG. 21 shows the composition of a filter of the type called IIR (Infinite Impulse Response Type) using feedback from output signal, and FIG. 22, FIG. 23 respectively represents the composition of filter combining them.
All these compositions are designed to perform the digital processing and, when analog signal input/output is necessary, require naturally AD converter and DA converter before and behind the input/output terminal but they are not shown.
The object of the present invention is, therefore, to provide a charge domain signal filter by recomposing with analog/digital mixed circuit the digital filter circuit that has been composed mainly of DSP such as FIR or IIR and introducing analog processing into the process of multiplication and addition consuming the most part of the power so as to reduce the total power consumption.